var nav = document.querySelectorAll('.nav > li');
var main = document.querySelectorAll('.main > div');

for(var i = 0;i<nav.length;i++){
    nav[i].index = i;
    nav[i].addEventListener('mouseover',function(){
        for(var j =0;j<nav.length;j++){
            nav[j].classList.remove('active');
            main[j].classList.remove('active');
        }
        console.log(this);
        console.log(this.index);
        this.classList.add('active');
        main[this.index].classList.add('active');
    })
}
